I finally got a chance to remove the transmission cover from my 1946 B to diagnose terrible racket that was occurring in 3rd and 4th gear (the worst is 3rd). To my dismay, the teeth on the 3rd sliding gear are badly worn (with only about 50% of the tooth surfaces remaining) with lots of chips. The 4th sliding gear is similarly worn and chipped, but not quite as badly.

I added about a gallon of kerosene to the transmission and drove it around for a little bit on Saturday, then drained it. I removed roughly a tablespoon of metal grit and fragments using a magnet pickup tool AFTER flushing with kerosene. The troughs for bearing lubrication were sludged up with thickened gear oil and metal chips. All is clean now, but I'm a little worried about the 3rd and 4th gears. I think I'm going to have to replace the sliding gears as well as their mating gears on the countershaft. And here I was hoping it was a bad bearing.